In a conventional magnetic storage system, a magnetic head includes an inductive read/write transducer fabricated on a slider. The magnetic head is coupled to a rotary voice coil actuator assembly by a suspension over a surface of a spinning magnetic disk.
In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined fly height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk. The fly height is the distance between the read/write elements of the head and the magnetic layer of the media.
One objective of the design of magnetic read/write heads is to obtain a very small fly height between the read/write element and the disk surface. By maintaining a fly height closer to the disk, it is possible to record high frequency signals to replace (high frequency signals), thereby achieving high density and high storage data recording capacity.
The slider design incorporates an air-bearing surface to control the aerodynamic interaction between the magnetic head and the spinning magnetic disk thereunder. Air bearing surface (ABS) sliders used in disk drives typically have a leading edge and a trailing edge at which read/write elements are located. Generally, the ABS surface of a slider incorporates a patterned topology by design to achieve a desired pressure distribution during flying. In effect, the pressure distribution on the ABS contributes to the flying characteristics of the slider that include fly height, pitch, and roll of the read/write head relative to the rotating magnetic disk.
In a conventional magnetic media application, a magnetic recording disk is comprised of several concentric tracks onto which magnetization bits are deposited for data recording. Each of these tracks is further divided into sectors where the digital data are registered.
As the demand for large capacity magnetic storage continues to grow, the current trend in the magnetic storage technology has been proceeding toward a high track density design of magnetic storage media. In order to maintain the industry standard interface, magnetic storage devices increasingly rely on reducing track width as a means to increase the areal or track density without significantly altering the geometry of the storage media.
Accompanied with the increase in the areal density of the magnetic media, the current trend in the magnetic storage technology has also been pushing the slider design toward a near zero fly height in order to reduce the magnetic flux spacing, thereby increasing the data recording capacity. Furthermore, to attain high linear or areal density, such a slider design may include a giant magnetoresistive (GMR) read/write sensor.
In principles, by reducing the fly height, the performance of the magnetic read/write head can be greatly enhanced, thereby enabling a higher signal to noise ratio (SNR) and lower read/write error rates.
However, in the conventional slider design with a near zero fly height, these advantages may not be fully realized due to a number of technical problems imposed by the operation of the magnetic read/write head with near zero fly height.
One such problem is the possibility of the read/write transducer coming into contact with the magnetic recording disk, which may consequently result in a catastrophic failure of the entire magnetic disk drive or head crash. The possibility of physical contact of the read/write transducer with the magnetic recording disk may be brought about by a number of causes, such as a thermal expansion process or low ambient air pressure associated with high elevation.
During a typical operation, the magnetic read/write head is subjected to various thermal sources that can adversely affect the magnetic read/write head. Both ambient and localized adverse heating effects of the magnetic read/write head will be described later in more detail.
Ambient heating sources are: 1) the heat dissipated by the motor that drives the magnetic recording disk; 2) a heat source results from the electrical power supplied to the VCM and drive electronics; 3) a small thermal source is attributed to a heat transfer process to the slider from the air friction generated by the rapidly spinning magnetic recording disk.
Localized heating effects arise from the operation of the read/write heads themselves. The write head has Joule heating input from the write current passing through its coils, as well as eddy current heating input from the eddy currents generated in its poles. The read head has Joule heating input from the read sense current passing through the GMR read/write sensor and a smaller amount of Joule heating from that current in the sensor leads. In general, the net ambient air temperature that the slider can experience may range from a room temperature of about (5° C.) to as high as 85° C.
The temperature increase consequently causes a thermal expansion of the pole tip region of the magnetic read/write head in all directions, but most adversely in the direction toward the magnetic recording disk. These thermal expansions, in effect, reduce the fly height, and in the worst-case results in a physical contact of the read/write transducer that causes a catastrophic failure of the magnetic disk drive.
Yet another problem also related to the near zero fly height is the altitude sensitivity of magnetic disk drives. As a magnetic disk drive operates at a higher altitude, the lower atmospheric pressure generates accordingly a reduced aerodynamic lift force. Consequently, the magnetic read/write head operates at a less than optimal fly height since the slider is not sufficiently lifted above the surface of the magnetic recording disk. In the presence of environmental temperature fluctuation, the risk of a magnetic read/write head contact therefore may become more pronounced.
On the other hand, the magnetic read/write head may operate at a fly height sufficiently distant from the surface of the magnetic recording disk. Even in the presence of the thermal expansion process, the fly height may deviate from its intended specification, but not low enough to present a head crash problem.
While the possibility of a head crash may be substantially alleviated, the performance of the magnetic read/write head may significantly suffer from the varying fly height. Since the magnetic permeability is proportional to the fly height, which affects the magnetic flux density, the deviation of the fly height may degrade the ability for the magnetic read/write head to register binary data onto the magnetic recording head. Furthermore, the variation in the fly height causes a varying performance of the magnetic read/write head, thus posing as a data integrity issue and a potential quality assurance problem.
To address this deficiency, a number of designs have been proposed. One such design utilizes electrostatic and piezoelectric actuators, this design would also require a complete redesign of the read/write transducer so it can be placed onto the movable part of a microactuator attached to the slider. Such a solution impedes the ability to optimize the design and current ease of fabrication process of the read/write transducer and therefore is less practical to implement.
Another design utilizing an active control method for head gimbal assembly was proposed in U.S. Pat. No. 5,991,114. The active fly height control is achieved through operating a gram load reducer between the support arm and the load beam to adjust the net force acting on the slider, which causes the slider to move closer to or farther from the surface of the magnetic storage disk as desired.
It is thus realized that the current attempts to address the control of the fly height of a magnetic read/write head still remains unsatisfied. It is therefore recognized that a further enhancement in the slider design for controlling the fly height of the magnetic read/write head is beneficial to the reliability and performance of a hard drive. Preferably, new slider design would afford all the advantages resulting from the near zero fly height, and at the same time would overcome the shortcomings with a conventional slider design.
Furthermore, the new slider design would achieve a controlled near zero fly height under most operational constraints. This in turn would result in performance advantages over the convention slider design.